Siddha, Suresh B wrote:> Andrew, Please don't apply this patch. This breaks the existing HT> (and multi-core) scheduler optimizations.> > Peter, on a DP system with HT, if we have only two runnable processes> and they end up running on the two threads of the same package, > with your patch, migration thread will never move one of those processes > to the idle package..

On a normal system, would either of them be moved anyway?

> > To fix my reported problem, we need to make sure that find_busiest_group()> doesn't find an imbalance..

I disagree. If this causes a problem with your "optimizations" then I think that you need to fix the "optimizations".

There's a rational argument (IMHO) that this patch should be applied even in the absence of the smpnice patches as it prevents active_load_balance() doing unnecessary work. If this isn't good for hypo threading then hypo threading is a special case and needs to handle it as such.

> > thanks,> suresh> > On Thu, Feb 16, 2006 at 11:39:34AM +1100, Peter Williams wrote:> >>Suresh B. Siddha has reported:>>>>"on a lightly loaded system, this will result in higher priority job >>hopping around from one processor to another processor.. This is because >>of the code in find_busiest_group() which assumes that SCHED_LOAD_SCALE >>represents a unit process load and with nice_to_bias calculations this >>is no longer true (in the presence of non nice-0 tasks)">>>>Analysis of this problem as revealed that the smpnice code results in >>the weighted load being larger than 1 and this triggers the active load >>balancing code. However, in active_load_balance(), the migration thread >>fails to take into account itself when deciding if there are any tasks >>to be migrated from its run queue. I.e. even if there is only one other >>task on the run queue other than itself it will still migrate that other >>task.>>>>The attached patch fixes that anomaly.>>>>Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>>>>>Peter>>-- >>Peter Williams pwil3058@bigpond.net.au>>>>"Learning, n. The kind of ignorance distinguishing the studious.">> -- Ambrose Bierce> > >>Index: MM-2.6.X/kernel/sched.c>>===================================================================>>--- MM-2.6.X.orig/kernel/sched.c 2006-02-16 10:51:52.000000000 +1100>>+++ MM-2.6.X/kernel/sched.c 2006-02-16 11:02:45.000000000 +1100>>@@ -2406,7 +2406,7 @@ static void active_load_balance(runqueue>> runqueue_t *target_rq;>> int target_cpu = busiest_rq->push_cpu;>> >>- if (busiest_rq->nr_running <= 1)>>+ if (busiest_rq->nr_running <= 2)>> /* no task to move */>> return;>>